Apparatus for resolving highly stable suspensions



April 1956 A. w. SADDINGTON ET AL 2,742,424

APPARATUS FOR RESOLVING HIGHLY STABLE SUSPENSIONS Original Filed Nov. 2, 1951 Sheets-Sheet l 7 23 so 23/ I L L 2 E5 55 2 ll 2o I9 lo J 24 1 25 I0 244 L 25] 3s 3 '39 7 48 73 T BO 40 42 g la;

45 45 |5- 53 .3 E1 FIG I r L W19 A.W, SADDINGTON I23 S,A.COLEMAN f INVENTORS i EMA/2 W AT TORNEY April 1956 A. w. SADDINGTON ET AL 2,742,424

APPARATUS FOR RESOLVING HIGHLY STABLE SUSPENSIONS Original Filed Nov. 2. 1951 5 Sheets-Sheet 2 A.W. SADDINGTON S.A.COLE MAN FIG.3

7)) ZS7VENTORS a). kg

ATTO NEY April 17, 1956 A. w. SADDINGTON El AL 4 APPARATUS FOR RESOLVING HIGHLY STABLE SUSPENSIONS 5 Sheets-Sheet 3 Original Filed Nov. 2, 1951 A.W. SADDINGTON S. A.COLEMAN INVENTORS ATTORNEY APPARATUS FOR RESOLVING HIGHLY STABLE SUSPENSIONS 5 Sheets-Sheet 4 Original Filed Nov. 2. 1951 S.A.COLEMAN INVENTORS FIG.5

ATTORNEY April 17, 1956 A. w. SADDINGTON ET AL ,7

APPARATUS FOR RESOLVING HIGHLY STABLE SUSPENSIONS Original Filed Nov. 2 1951 5 Sheets-Sheet 5 fire. .14.

fire. .15.

A WSflDD/A/GTO/V, .5: A 5 OLE/144W,

INVENTORS.

. 2,742,424 I APPARATUS FOR RESOLVING HIGHLY STAB E r ,SUSPENSIONS p i I Arthur W. Saddington and Spencer Coleman, l

. D .La Mesa, Calif. v Original application November 2 1951,. SeriaLNd.

' 254,603. Divided and this application June 24, 1952,

Serial No. 295,322 g i r a 19 Claims. ((21.210-53 This application isia division of our application bearing the same title, filed NovenrberZ, Q1951,'under Serial No. 254,603. I e M In the copending application of A. Wl Saddington and G. R. Tully, Jr., entitled Method of Clarifying Crude Solutions of Alginates, filed November 2,, 1951, under Serial No. 254,602, now abandoned,thel subject matter of which, however, has notbeen abandoned and is now' described and claimed in a co-pending continuation-inv 2,742,424 Patented Apr. 17, i 1956 8 is a vertical section througha skimmer arm and the attached 'skimme Fig. 9 is a fragment-a1 elevation of a skimmer arm and,

the attached skimmer, illustrating the suspension of the skimmers from rollers resting on tank flanges;

Fig. 10 is a diagram illustrating the travelof'the skim- I met blade up the ramp 68 and'over the further edge of trough 66;

Fig. 11 is a cross section through one of the bottom p s. 1 g

. Fig. 12 is a fragmental face elevation of the same;

Fig. 13 is a diagram. illustrating alternative connections to a device for controlling liquid flows by means of a manually adjustable'swing pipe;

Fig. 14 is a view similar to Fig. 2 showing a modificationof the apparatus; and

Fig. 15 is a view similar to Fig. 13 illustrating the same modification.

part application .filed by said applicants on January 10,-

1955, under Serial No. 480,978,]there is fdescribeda process directed to the rapid. and economical separation of v oellulosic residues from the solutions of water-soluble Jalg inicsalts resulting from 'the digestionofakelps with aqueous alkaline solutions, thismethod being capable of, V performancein apparatus known to the prior art- Reference is first made to Fig. 1, showing an assemblage of apparatus in which the invention is embodied. In this figure, iii-10 indicates a plurality of storage tanks;.11 a

feed tank in which the liquid to be treated is maintained at constant liquid leveland at constant viscosity-12 is a primary aerator in which the feed solution or, crude liquor is intimately blended with air, and 13 is a primary separating cell in which the major part of the suspensoid originally contained in the crude liquor is separated as 7 mild fractions.

? vThe primary purpose of 'the' present invention is to provide 'a'more elfective and less costly apparatus for car:

tying out the above method than has heretofore been.

known, this apparatus also being applicable in other situations in which parallel, conditions and limitations .are encountered.

j A purpose of the invention is to provide apparatus for separating finely divided solids or organic semi-solids from suspension in liquids which have ,a specific gravity only slightly less than thatof the suspensoid.

A purpose of the invention is "to providemeans for separating semigelatinous solids from su'spensiou in relatively viscous liquids.

v A purpose of the invention is to provide apparatus in which suspensions of solids, particularly such as are of L substantially uniform particle size and specific gravity,

are subjected simultaneously to flotation and to sedimen tation for the more complete and rapid removal of the solids than is possible .with the application of either elfect alone. p

The invention will best be understood with reference to the attached drawings and the following description thereof, in which:

Fig. 1 is a diagram showing an assemblage of apparatus in which the invention is embodied, this figure showing 4 also the flows in an operation in which the apparatusis 14 is a secondary aerator in which the mods drawn from theprimary cell are strongly diluted with water" and intimately blended with air; 15 a secondaryseparating cell in which the major part or substantially all of the 1 suspensoid present in the primary muds is separated from a se'condary liquor containing most of anysolute presentin these muds; 16 a conduit for withdrawing the primary liquor, at least partially freed from suspensoid, to a point of disposition, as for example to a filtering station; 17' is a conduit for withdrawing muds from the secondary separator to a point of disposition, as for example to waste, and 18 a conduit for returning the secondary liquor;

to the intake end of the system to dilute the entering supply of suspension.

When the suspension to be separated originates in an alginic digestion product, which is normally of a pasty or highly viscous consistency, of variable alkalinity and liable tobe contaminated by sand, shell fragments and other heavy solids which would interfere with subsequent operations, the tanks 101li provide a locus for dilution of the product to the point at which the heavy solids-will settle readily and for any needed pH and viscosity adjustmerits. In the handlingof suspensions not requiring such used forthe separation of cellulose from a crude alginic,

solution;

Fig. 2 is a plan view of one of the separating cells 13 or 15 with all moving parts removed, taken onthe line 22 of Fig.3;

"Fig. 3 is a vertical section and partial internal elevation of the shell, taken 'on the broken line 3"3 of Fig. 2; i

Fig. 4 is a sectional and fragmental extension of the launder 74-or" Fig. 3; f 1

Fig. 5 is a fragmental plan view of the skimmer spider 88.90, taken. on the line 5--5 ofFig. 6; a Fig. 6 is a vertical section through one of the'separating cells, as on the line 6'6 of Fig. 5, illustrating theskimmers and bottom rakesin operative relation; I Fig. 7 is a plan view of the bottom rake assembly, as on the line 7--7 of Fig. 6;

- preliminary steps, these tanks may be omitted, or a single tank may conveniently be used as a surge tank;

In the use of the apparatusfor its primary purpose, the clarification of crude alginic solutions, a stream of thedigestionproduct from digesters or macerators not shown enters the. system at 1% and is mixed in a pump'lli with astream of a highly dilute alginate solution (the secondary liquor) returning from thesecondary, separator 15 through conduit 18 and branch conduit 21. The di luted product passes through conduit 22 and valved branches 23'23 into one or the other of the tanks 10,

from which the settled sand is removed from time to time as indicated at 24.

At this point the diluted product is an aqueous solution of a water-soluble alginate, usually sodium alginate, containing a large-proportion (for example, 60% to 80% of the algin content) of finely divided cellulose resulting from the breaking down of the kelprstructure during digestion, together with a lesser but variable proportion of solid, water-insoluble alginic materials of variable com- '-position. These insoluble solids travel through the sys- 3 tem with the cellulose, up to the secondary stage of separation, in which they may disappear by passing into solution, and are considered to be a part of the cellulose in the ensuing description.

A stream of the diluted solution is drawn from one or the other of tanks 1 0--10, used alternately, through conduit by a pump 26 in which it is blended with the remainder of the secondary liquor, drawn from conduit 18 through branch 27 The solution then passes through conduit 28 into, feed supply tank 11 in which a constant liquid level is maintained by an overflow line 29 and valved branches 30() or by control of the delivery of pump 26. The degree to which the solution is dilnted in these steps is controlled initially by varying the ampnnt of fresh water introduced into secondary aerator 14 through conduit 31, and finally by a viscosity control later described.

A stream of the solution passes continuously, preferably by gravity, from tank 11 to primary aerator 12 through conduit 32, in which valve 33 is a stop valve only. It'is highly important to'the success of the primary separation that the viscosity of the feed stream be controlled within very narrow limits, as for example Within 1 centipoise'on either side of the viscosity which has been fixed on as optimum for the operation on the material being treated.

Control of the water supply to the secondary aerator will maintain a close approach to the permissible limits, but because of the quality of solution always present in the secondary separating stage, the response to changed adjustment at the aerator is slow. To take up this lag we insert in feed conduit 32 a continuous viscosimeter indicated at 34, which is connected to actuate a valve 35 controlling a small flow of fresh water through conduit 36 into conduit 25 and thus into tank 11 With proper attention to manual regulation of water flow into the secondary aerator, the quantity of water introduced this manner directly into tank 11 rarely exceeds two percent of the flow out of the tank and averages nearer one percent.

An instrument adapted to the control of this small water stream, and illustrative of the type of device best adapted to this situation, is the Viscotrol manufactured by Brookfield Instrument laboratories. In this instrument an inverted cup or drum suspended by a torsion wire is rotated at constant speed in a bath of liquid bypassed out of the feed stream, Electrical contacts arranged to be opened and closed by changes in torque, control solenoids which in turn open and close valves admitting air to opposite ends of a pneumatic cylinder containing a piston linked to the valve which controls the water supply (valve 35 of Fig. 1).

The cellulose suspended in the crude liquor is difficult to remove by air flotation, and the ensuing flotation step will not be performed most etfectively unless the aeration means divides the entrained air into extremely minute and correspondingly numerous bubbles. While the invention contemplates the use of any preferred aeration means, we have found that the prior art apparatus does not give the best results in this difficult service and have therefore devised an improved aerator by the use of which the proportion of cellulose removed in the fiotation step is materially increased. i

This device consists essentially of a continuous delivery liquid pumpcentrifugal, turbine, gear, vane or multiple piston-capable of raising the liquid to from 20# to 80 gauge, in series with a turbulence-producing element+a high speed centrifugal or turbine pump or any mechanical beater adapted to operate under pressure-with means for introducing into the discharge of the liquid pump a stream of air under pressure sufficient to overcome the liquid pressure. The air thus introduced between the two main elements tends to destroy any effectiveness of the second stage (turbulence) element as a pressure-raising means, but causes a turbine pump or a straight blade centrifugal to produce extreme turbulence in the fluids supplied to. it,

and consequently an extremely fine dispersion of air throughout the liquid. -With this arrangement, the suc tion of the primary pump will not break unless the air supply be grossly overloaded.

A convenient embodiment of this device is shown schematically at 37 in Fig. l. This is the well-known, ul i ta e d e w ll th hin pump which, for this P. u rpose,must have not less than two stages and preferably a considerably larger number, and which should be capable f is ha gin a ins a h ck messux not less than 20# gauge while being supplied with air. The pump is arranged o draw i s liquid .shpply rom a s l 5. n which he ke 1 9 9 the Pum i shh n sedp nd l e s in a discharge chamber 39.

The air supply, from a source not shown, enters the pump through conduit 40, at a level at which the liquid has reached the desired pressure, for example, into the second orthird stage from the delivery end.

a We have found that the effectiveness of the flotation step is materially increased by utilizing the process deib in U- lh e 1 37 59 to N l ssie s h asing he iqi i to d ssolve i wi e P s r an h e.- after releasing thepressnre to cause the air to be evolved in minute bnbblesj We therefore pass the mixture of air and liquidfrorri pump discharge chamber 39 through u 41, to a r t nt o ham e of suc paci as to provide'liquid retention of more or less five minutes, This chamber may be'a standpipe as shown or may be any stilt able enlargement of the discharge conduit.

' he uid l avi t e ppe end of the amber p s h 'ii h co du .3 to an a rap 44 wh ents any i which i the c a s u di ded to be a ne by he flowing q sl- Thi ma be. n tea p a ing its ch s t n's rea an e en r as h q i lcvcl falls rat er han o ven i id as he e l i Th amount of air vented from the trap affords a guide for the manual control of the air supply at valve 45.

It is essential to the best operation of the separating cells 13 and 15 that the feeds of aerated liquor to them be in constant volurne. Even a minor degree of surging, such as may not prevent the clean separation of the ter o fiqta i mu will e nd si p de he sedimentation by which the bottom mud is separated, increasing the proportion of cellulose passing out with the primary liquor and the proportion of algin passing out with the primary bottom mud. We avoid surging and its attendant disadvantages by restricting the feed stream to a constant cross-sectional area maintained at a constant pressure.

For. example, a fitting 46 retaining an orifice plate having, preferably, a sharp-edged orifice, is placed in conduit 43, the area of the orifice being such as to pass the required volume at the preferred pressure. The pressure upstream from this orifice is stabilized by a suitable pressure regulator, for example a throttling valve 47 actuated by a diaphragm or bellows 48 which in turn is responsive to the pressure in the feed line above the orifice, asind ic ate d at 49. By this means a feed of constant volume to the separating cell is assured, this feed P g hl t e QI PQ at sp mx ta e t o p r c pressure, into a feed distributing box 50 which is an ele- 9 Qt ach ht he-sspar tih @911313 and 1 In separating cell 13,, the construction and operation of which are described at a later point, the stream of crude liquor is fractionated into three product streams: of P mar iqhqi leaving e e l. u h @9 1- d t 68$ the. qdhst t h eration. t is in a relatively concentrated solution of sodium alginute con: taining from 25% down to a trace of the original cellulose content of the crude liquor-7; (2) a top. mud" produced by flotation, leaving the cell through conduits 51-,51, and (3) a bottom mudproduced by sedi mentation, leaving the cell through conduit 52.

The two. muds from the primary cell, cqntainingfrom to substantially all of the cellulose of the crude liquor, are combined in'conduit 53 and pass to the secondary aerator inwhicli the mixed mud is blended with fresh water from conduit 31. The quantity of water is regulated to produce at least approximately the desired degree of dilution of the crude liquor in tank 11 when returned thereto in the secondary liquor. An addition of alkaline solution for control of the pH value of the bothrichin cellulose and lean in algin, which. are col snoseclj :lectedin conduit. 17 and discarded or otherwise of, and a dilute solution of sodium alginate substantially free from cellulose, the secondary liquor, which is returned, to tanks 16 and '11 through conduit 18.

The separating units 13 and i5, may be identical or closely similar in structure, though as separation in the secondary stage is more rapid than in the primary, cell 15 may be smaller than cell '13, or two primary cycles may be provided to feed mud into one secondary. The structure of these units is illustrated in detail in Figs. 2 to 13 inclusive,'reference beingiirst made to Figs. 2 and 3.

The basic unit of the cell is a relatively wide andlow, open cylindrical tank having a gentlyisloping bottom. This tank may be constructed of any preferred materials, but it will be found economical and otherwise desirable to use a metallic ring wall 69 sealed atits lower endinto' a concrete block '61 of which the upper surface, forming the tank bottom '62, slopes 't'oward a central Well '63. Tightness is produced by a 'su'rface layer 64 of fine grained concrete, applied'after 'th'ebody of the block has hardened.

Inside the shell-ring and concentric with it is a battle ring that divides the tank into an outer circular into'which clearor relatively clearliquor'overfiows and from which it is drained by conduit- 16 (of primary cell 13)or conduit 18 (of secondary cell "15). The floor of this launder should draintowardthe outlet opening. It is desirable to extend a:sloping skirt 74 from the lower corner ofthe launder to the bafiie wall to avoid mud accumulations. v l

The launder is shown on a larger scale in Fig. 4, in

section and also in fragmental extension. 'The upturned edge of the trough is provided with an overflow wall or weir of thinstainless steehthe upper edge of the weir being serrated as at 76. This element maintains the liquid'level 69 within the limits fixed by the depth of the serrations, indicated by dotted lines 77-78, or at least. I so long as the withdrawal of bottom mud by means later described is not too rapid. The limits 77-78 in turn fix the relative height offramp 68. (see Figs. 3 and 10), which 7 'must extend above and below these limits.

flotation compartment and an inner circular overflow compartment. The ring63 is supported and spaced from the shell by a plurality (preferably four) of top rnu'cl collecting troughs 66, welded at their opposite ends to .the shell and baffle respectively. These troughs terminate 'atthe lower edge in a drainage trough 6'? which slopes outwardly and delivers the top muds into collecting conduits 5.1.

in addition to supporting-the baffle ring, these troughs serve a dual purpose: toreceive and carry away the mud produced by flotation, and to support the feed pipes 7ll-7l with the minimum of horizontal surface below liquid level. Such surface, whether upwardly or down wardly directed, tends to accumulate mud deposits and to suddenly release them, withscvere disturbance of the separations. The V-shape of trough 66 also is designed to avoid accumulations of this kind.

The edge of each trough which is'first encountered by the rotating Skimmers is provided with a sloping ramp 68, the lower edge of which is below and the upper edge above the liquid level indicated by dotted line 69.

The feed of crude liquor is introduced into the annular space between shell and battle by any means which will distribute the feed over the width of the annulus and deliver, it into the liquid body with the minimum of disturbance. This means, which obviously might take diverse forms, is here illustrated as consisting of conduits '7il"lll which are closed at the end adjacent the bafile ring and are provided with branch pipes 71-9-71 extending through the wall o f the trough and terminating in The upper edges of shell and bafile ring are provided with flanges 79 and 36 for the support of'the rotating skimmer elements now to be described with reference. I to Figs. 5, 6, 8 and 9. 1

Referring first to Fig. 6, 'a central vertical shaft 81 isrnounted on a' step bearing 82 fixed to the bottom ofwell 63. The upper end of the shaft runs in a bearing 83 carried in anyconvenient stationary structural member 84 which may well be an element of a platform over the tank.

The shaft may be rotated by any means which will give a smooth and positive drive, free fromhunting or jerking, for example by a bull wheel 85 of the greatest possible diameter. This bull wheel may be aspur, bevel or worm 'geaiy bu't foreconomy in construction we prefer to weld a circle of angle iron to the skimmer arms described below and to tack weld to thevertical leg of the angle a continuous band of ,roller sprocketchain 86.

The bull wheel is driven by a sprocket pinion 87 from 7 any source of power not shown,.preferably an individual electric motor. O

. The upper portion of the shaft carries two discs 88 and 89; keyed or welded to the shaft, and a plurality of radially directed skimmer arms 9tl90 are welded between the discs at their inner ends. These armsare preferably constructed from pairs of channel members 9191 (see Fig. 8), spaced apart at suitable intervals as by blocks 92 and evenly spaced radially by attachment to bull wheel 85.

At about the locations indicated in Figs. 5 and 6, slide blocks 93, placed between the channels, are supported on pivot pins 94 entering corresponding depressions in the block, which is thus free to swing in a vertical plane longitudinally of thearm. A slide 95 having an enlarged head 96 is mounted in a vertical bore formed in the block.

The lower end of the slide is flattened, as at 97, to pass between the arms of a yoke 98 in which it is pivoted on a pin 99. Thus mounted, the slide, to which the skimmer is attached, is free'to rise and fall and also to swing in a vertical radial plane.

The yoke 98 has a base plate 100 carrying two thin;

L-shaped elements 101 which grip a strip of rubber or f other flexible material 182. This strip extends from the inner wall of tank shell 6t) to the outer wall of baffie ring The two pivots 94"and d9 permit this skimming element to move laterally in the annulus between tank wall and balfle ring and thus tofollow any irregularities in contour of the tank shell. It is much easier to .bring the bathe ring into .parallelism with a somewhat out-of round tank shell than to build a large diameter tank to a true circle.

Each skimmer has at each end a bracket 103 (see; i

Fig. 9) attached tothe upper face of yoke plate. 100, these brackets carrying pins 194 on which rollers 105 are free to revolve. flanges 79 and 80, these flanges forming tracks which are level except at the points (e. g., Alin Fig. 10) 'where These rollers normally rest on the shimmers approach ramp 68. Between thehumps' later referred to, the flanges and rollers support the-skimmeniblade 101 infla position in which it dips a short distance below the liquid level ,69 in the tank.

As the blade approaches the lower edge of ramp 68, the rollers ride up the slope of hump element 1% affixed to each track, carrying the blade up the sloping upper surface of the ramp and over its farther edge, after which the blade dips it into the liquid gently and without disturb.- ing the .upper layer of top mud.

The device just described may be modified by replacing the enlarged head 96, as shown in Fig. 9 by a large threaded nut as at 96' in Fig. 8. This modification has twoadvantages: first, that it permits the effective length of slide .to be so adjusted with respect to the height of bracket 103 that the rollers 105 will not rest on the level portions of the flanges 79 and 8.6 but will clear them slightly, engaging only the humps 16.6. This will avoid any difficulty otherwise experienced in making the tank and battle ring flanges smooth and level.

A further advantage of this modification is that it permits an adjustment of the depth to which the blade dips below the surface of the liquid, thus skimming off all. of the top mud with the least disturbance of the liquid immediately beneath it.

The final moving element in the separating unit is the bottom rake, which moves the bottom mud into central well 63. This element is shown in elevation in Fig. 6 and in plan in Fig. 7, with certain details of construction illustrated in Figs. '11 and 12.

A collar 197 is fastened to shaft 81 adjacent its lower end and two arms 108 are hinged to the collar as at 1419. A second collar 110 is fastened to the shaft at a higher level and horizontal struts 112 are projected from it at right angles to the arms. Truss rods 3.13 connect the ends .of these struts with the ends of the arms. The truss rods should be provided with means for varying their effective length, for example a lug 114 projected from the arm and a nut 115 threaded on the rod and engaging the ug.

This arrangement of struts and truss rods provides for supporting arms 108 in position parallel with the tank bottom and forms with the arms a rigid spider. The purpose of rigidity is to prevent hunting of the arms which, if permitted, would tend to disturb the extremely light bottom mud, Only two arms 168 are shown in Fig. 7 but any larger number may be used and arranged in the same general manner.

The wipers 116, in any required number, are hinged to the lower side of each arm and at an angle to its axis, this angle preferably being not less than 45 of mounting the wipers is illustrated in Figs. 11 and 12.

A plate 117 is notched to receive the lower half of the arm 108 at the desired angle, and is welded in place. The wiper assembly 116 includes this plate, a second plate 118 swinging on a long pin 119, a strip of rubber or other flexible material 120 and a metallic strip 121 clamping the rubber in place. The height of arm 1% is so adjusted that the wiper meets the tank bottom 62 at a slight angle to the vertical, trailing the arm, and a weight 122 projected rearwardly from plate 118 holds the wiper in contact with the bottom while permitting it to ride over slight irregularities in the surface.

The spacing of the wipers on the arm should be such that the entire tank bottom is swept at least once and prefe 'ablyv twice at .each revolution of the rake assembly. The .cellulosic muds separated from alginic solutions are excessively subject to bacterial action if allowed to collect for more than brief periods, this action resulting in severe depreciation of the quality of the algin. Thus it iscssential that the bottom be kept free from any lasting collection of sediment, even in restricted areas. The ute mo t w pe n each rm h uld reach o t e mm diate edge of the tank bottom and the innermost element on the same arm to the edge of well 63, the intermediate The method 8 wipers being so spacedthat the area's swept by them overlap at least slightly. .With this arrangement each arm sweeps the entire tak bottom at each revolution.

It is highly desirable that the rate of drainage of the bottom mud be as nearly constant as possiblewh'ile being subjected to control for the adjustment of the relative quantities of bottom mud and clarified liquid flowing from the tank. A convenient device for this purpose is shown in plan at 123 in Fig. 2 and in internal elevation in Fig. 13. i

The overflow illustrated includes an open top box or tank 123 attached at any convenient point on the circumference to the exterior tank face wall 60, the upper edge of the box being approximately level with the top of the tank. This box is provided with two pipe connections, one (as at 124) terminating at the bottom of the box, the other (as at1'25) extending through it and supporting a swing pipe 126 on any swivelling coupling means 127.

One of the pipes 124-425 is connected with the conduit (53 or 17 of Fig. l) by which the bottom mud is conveyed to the next element in the system; the other with conduit 52 which drains the mud from central well 63. In Figs. 2 and l3, it is assumed pipe 125 is connected to conduit 53 and pipe 124 is connected to conduit 52. Either order of connection may be used, but the functioning of the device is not exactly the same in the two instances.

Thus, if pipe 125 is connected with conduit 52 and pipe 124 with conduit 53, as shown in Figs. 14 and 15, the how of mud is from the swing pipe into the box, and by the provision of a manual valve 128 in pipe 124 it be comes possible to gauge the flow of mud from the tank by closing the valve and noting the time required for the box to fill.

The ability to make this measurement is a convenience, but we have noted some tendency for mud outfiowing in the swing pipe to accumulate deposits which choke the flow and disturb smooth operation. Such choking is much less likely to occur when the connections are reversed and the flow is out of the box into the swing pipe, provided this pipe discharges into a conduit of ample size and free from serious obstructions.

With either order of connection, the swing of pipe 126 must be such that its free end will traverse the depth of the serrations 76 of launder 74, these serrations and the swing pipe cooperating to fix the tank liquid level 69. The height of the launder being fixed, adjustment of the position of the swing pipe will vary the relative quantities of clarified liquid and bottom mud flowing from the tank, and thus permit the mud to be held at the most desirable concentration of solids. Ordinarily this will be the maximum solids content at which the mud will flow steadily from the tank. The quantity of top mud removed by the skimmers is little if at all affected by variation in liquid level, this quantity varying with the effectiveness of the flotation step and the proportion of solids capable of removal by flotation.

Assuming that the pipe 125 is connected to the conduit 53 and pipe 124 is connected with conduit 52, the operation of the separating unit will be follows:

The crude liquor is fed by four feed pipes 73 to the four conduits 70 inside the troughs 66 and passes through the various branch pipes 71 to the Ts 72 for flow into the outer annular flotation compartment defined by the bafile ring 65 and the outer peripheral wall 60 of the unit. Flotation mud is swept by the skimmer blades 101 up the ramps 68 into the four top mud collecting troughs 66. The top mud drains from the troughs 66 into the collecting conduits 51 for withdrawal from the unit.

The liquid separated from the top mud flows gently under the baffle ring 65 into the inner circular overflow compartment formed by the battle ring. The bottom mud settles on. the sloping tank bottom 62 and is urged by the bottom wipers 116 into the central mud well 63 where the bottom mud enters the conduit 52. The conduit 52 carries the bottom mud to the pipe 124 to deliver the bottom mud into the open top box'123 that is approximately at the level of the top of the tank. The topmud the apparatus-and its manipulation as to-remove the maximum proportion offthe suspensoid in the flotation step. I

This, because the sedimenting eifect is inherently slow and is highly sensitive to disturbing influences, but is greatly accelerated by progressive reduction in the proportion of suspensoid remaining after flotation.

The top or flotation mud from crude alginic liquors and other suspensions of like character is very light, rises rapidly to the surface and is not readily redispersed in the liquid from which it separates On the other hand, the attachment of the buoyingair bubbles to the solid particles is temporary and thus the maximum removal by. flotation requires that the top mud be skimmed ofi before any large proportion of the solid particles lose their air bubbles and begin to subside. e

Incontrast to the. above, the sedimentation mud will remainlindefinitely on the tank bottom if not disturbed but, because of the extremely slight gravity difference between thesuspensoid and the liquid, the sediment layer is'very unstable and is readily redispersed in'theliquid from whichithas been deposited. Y Y i .The above considerations are governing in arrivingat -optimum proportions numbers and operating speeds of various elements of the separating cells.

It should becautioned that it is possible to carry this multiplication of skimming effects too far; lf'insuflicient time beallowed in each segment of the upper surface,

as defined by the space between troughs, for a material To avoid redispersing the bottom mud it is essential to rotate the bottom rakes at a very low speed and in such manner that the tip speed of the arms will becompletely uniform, free from hunting or jerking. In an illustrative cylindrical cell of .feet diameter we prefer to rotate the bottom rakes at about one revolution per hour, or between the limits minutes to 80 minutes per complete revolution. This is equivalent to top speeds from 50 to 125 feet per hour, which may be taken as a guide to rates of rotation in tanks of other diameters.

At such rotative speeds, the removal of top mud by a single skimmer moving the mud into a single collecting trough is far too slow, the mud remaining on the upper surface so long that a large part of the buoying air bubbles become disengaged, with loss of a correspondingly large part of the value of the flotation step in accelerating sedimentation.

While it is possible to drive the rakes and the skimmers at different speeds, thisis undesirable as tending to considerable complication of apparatus. Further, speeding up the skimmers increases turbulence in the top mudlayer and unduly rapid disengagement of air bubbles. "We therefore prefer to provide for the prompt removal of top mud by multiplying both the numberof collecting troughs and the'numberof'skimmers, thus'producing a multiplicity of removals of top mud with each revolution of the skimming assembly and of =the'bott om wipers,

permitting the 'two elements to rotate at the same speed.

Wehave found that inacell of about'25 feet diarri eter, the number of collectingtroughs 66 should .be not less than three and preferably four, or in cells of other diameters the optimum number may be found by dividing the cell diameter in feetby six or eightand taking the nearest whole number. The number of individual skimmers shouldbe greater than the number of collecting troughs,'not less than double and preferably two and one-half or three times the number of troughs' Y part of the liquid to settle out of the mud layer, the eftank. The wiperarms 108 should, be hollow andv of sufficient diameter to be stifi when tied together at their f ends only, oran additional set of tie rods 114 may be,

used at midlength of the arms. The prime mover should be a constant speed element, as for example a synchronous motor, and any speed reduction or control between this motor and sprocket 87 should be positive, avoiding chains or belts which might tend to whip. The angle iron ring which is the basis of the bull wheel should be stilf and the chain 86 should be drawn tightly around it and tacked at such short intervals'as to avoid risk of local creeping or bulging.-

The, proportionate'dimensions of the fixed elements of the cell are highly important in producing the 'greatestloverall. separation of suspensoid from a liquid very nearly as heavy, as ,the'suspensoid, and particularly from a viscous liquid] M g I First, the enclosing-tank should be relatively wide and shallow, to'spread the flotation mud into a thin layer and to minimize the distance through which subsiding particles must travel before-they come to rest. The best results will be attained when the inner height of the tank wall is-not more than one-fourth and preferably about one-fifth of the diameter of the tank. 7

Second, the bafflering 65 which divides the inner cylindrical compartment from the outer annular compartment,

should have a liberal clearance from the tank bottom; This ring, which necessarily projects above the surface of the liquid body in the tank and therefore has its upper edge more or less level with the tank rim, should have a height not greater than six-tenths and preferably not greater than four-tenths the height of the tank wall. This allows space for the suspension flowing from the outer to the inner'compartment to reverse its direction of vertical flow without disturbance of the sensitive bottom mud.

Finally, the horizontal area of the annular outer compartment should bemuch greater than that of the cylindrical inner compartment, not less than four times and up to eight times greater.

. In the inner compartment the direction of liquid how is counter to that of particle movement in settling and, as the settling rate of these fine suspensoids is low, this compartment has only a minor and often no'value for sedimentation, functioningmerely as an overflow conduit. I I

'In the annular outer compartment the liquid flows downwardly, accelerating deposition of solids'and making this portion of the tank highly effective for sedimentation; Thus, while the increase in upward velocity resulting from narrowing the inner compartment increases the tendency toward'carry over of such solids as enter its lower end, the accompanying widening of the outer compartment far more than offsets this disadvantage by increasing the extent of deposition and thus reducing the proportion of suspensoid entering the inner com- '1 1 cal as defining conditions producing maximum separation. In the handlingof other suspensions to which the apparatus may be applied, these limitations should beconsidered as suggestive rather than critical;

In the separation of cellulose from alginic solutions in which the values are in the algin solute, in which the cellulose is substantially or entirely waste, in which the solution is initially too viscous to be handled without dilution and in which excessive dilution of the liquor must be avoided, the use of the two stages of separating apparatus is essential to the recovery of a feasible proportion of the original algin content without diluting it to the point at which the recovery of the algin from the clarified solution would be impracticable.

In the separation of generally similar suspensions which are initially of low viscosity or in which there is no limit to the extent to which dilution can be carried, it is often feasible to use the first stage apparatus alone, either to accomplish the final result desired or for a preliminary treatment in advance of other separating means such as filters, centrifuges or simple settling tanks.

The major utility of the apparatus is in the separation of suspensions such as alginie solutions, in which severe depreciation of the quality of the solute results from bacterial action at relatively low temperatures or from depolymerization at temperatures at which bacterial action is inhibited. These are progressive reactions, which are reduced'in undesirable efiect in direct proportion to any shortening of time under treatment.

,In this respect the described apparatus, when operated under suitable conditions of viscosity andtemperature of solution, produces a result which has not heretofore been attained in the clarification of algin solutions.

So large a proportion of the total cellulose is separated by the primary flotation, and the subsequent sedimentation is so accelerated thereby, that the residence of the solution in the primary stage, from which the greater part of the original algin is withdrawn, is reduced far below that required in any separating method heretofore used.

For example, the residence of the solution in the primary stage need not exceed one hour, even with the minimum dilution of the liquor and the consequent minimum cost of recovery of the algin from the clarified liquor. T his reduction in clarifying time minimizes the reduction in viscosity-producing value of the final product of soluble alginic salts which is inherent in any clarifying process, and makes it possible to produce higher viscosity and more valuable alginic salts than any heretofore produced and at a less cost for apparatus, for clarification and for subsequent treatment.

We claim as our invention:

1. Apparatus for separating finely divided solids from suspension in a liquid only slightly lighter than said solids, comprising: a relatively wide, open, cylindrical tank having a vertical wall and a bottom outlet; a baffle ring concentric with said wall and dividing a cylindrical inner compartment from an annular outer compartment, said ring extending above the liquid level in said tank and being spaced from the tank bottom; a plurality of flotation mud receiving troughs radially arranged in spaced relation within said annular compartment and means for continuously draining said troughs; means for feeding said suspension into said annular compartment between said troughs; a plurality of Skimmers arranged within said annular compartment and means for causing said Skimmers to rotate around the axis of said tank to urge flotation mudinto said troughs; means for continuously draining clarifiedliquid from the upper side of the liquid body in said cylindrical inner compartment; means for continuously sweeping sediment collecting on the bottom of said tank to said outlet, and means for continuously withdrawing said sediment from said outlet while maintaining a substantially constant liquid level in said tank, I

2. Apparatus as described in. claim 1, in. which the ing elements to hold the same in contact with the tank 12 inside height of said vertical tanlcwall is from one-fourth to one-fifth the inside diameter of said tank.

3. Apparatus as described in claim 1, in which the spacing of the lower edge of said baflie ring from said tank bottom is from four-tenths to six-tenths of the inside height of said vertical tank wall.

4. Apparatus as described in claim 1, in which the area of said cylindrical compartment, measured horizontally, is materially lessthan the area of said annular compartment.

5. Apparatus as described in claim 1, in which the area of said cylindrical compartment, measured horizontally, is fromone-fourth .to one-eighth the area of said annular compartment.

6. Apparatus as described in claim 1, in which the number of said flotation mud receiving troughs is the whole number nearest to the quotient of the diameter of the tank in feet divided by a number not less than six nor more than eight.

7. Apparatus as described in claim 1, in which each said flotation mud receiving trough is provided with an inclined ramp extending below liquid level and projected upwardly and inwardly from the edge of said trough first encountered by said Skimmers and over a portion only of the width of said trough.

8. APParatus as described in claim 1, in which the ends of said flotation mud receiving trough are nonleakably.

attached'respectively to the outer face of said bafile ring and the inner face of said tankwalland the drainage means is a conduit extending through the tank wall from the lowermost portion of said trough.

9. Apparatus as described in claim 1, in which said feeding means is connected with said tank at radially spaced points adjacent said flotation mud receiving trough and at the side thereof last encountered by said rotating Skimmers.

10. Apparatus as described in claim 1, in which said feeding means comprises a conduit located within said trough and branches extending from said conduit through the wall of said trough on the side last encountered by said rotating Skimmers.

11. Apparatus as described in claim 1, in which the clarified liquid drainage means includes a launder arranged around the inner face of said bafile ring, the upper inner edge of said launder being horizontal and serrated.

12. Apparatus as described in clain 1, in which said sediment sweeping means includes a rotating vertical shaft centrally disposed in said tank; radial arms afiixed to said shaft to be revolved thereby; means for independently raising and lowering the outer ends of said arms to adjust their angle with the tank bottom; wiping elements hinged to the lower sides of said arms and arranged at such angle to said arms as to urge said sediment toward the central point, of the tank bottom as said arms rotate, and weights projected from the trailing faces of said wipbottom.

13. Apparatus as described in claim 1, in which the skimmer rotating means and the sediment sweeping means are actuated by a common, vertical shaft centrally disposed in said tank; a bull wheel of relatively great diameter attachedto skimmer arms projected from said shaft and forming with said arms a rigid spider, and a positively driven toothed pinion meshing with depressions in the periphery of said bull wheel.

14. Apparatus as described in claim 13, in which the diameter of said bull wheel is from seven-tenths to ninetenths the diameter of said tank.

15. Apparatus as described in claim 1, in which said sediment withdrawing means includes a conduit communicatingwith the central point of the tank bottom and extending to approximately the level of said clarified liquid draining means, the height of the outlet end of said conduit being adjustable to vary the relative liquid volumes passing respectively through said sediment withdrawing means and said clarified liquid draining means.

16. Apparatus as described in claim 1, in which the number of individual skimmers is from two times to three times the number of said flotation mud receiving troughs.

. compartment; means for continuously draining said trough means; means to skim flotation mud in said flotation compartment into said trough means; anoverflow wall for discharge flow of clarified liquid from said overflow compartment, said overflow wall determining the approximate liquid level in the tank; and means to draw off sediment from said bottom outlet, said draw oif means including passage means with a discharge end terminating at approximately the level of said overflow wall, said discharge end being adjustable in height to vary the, rate of flow therefrom relative to the rate of flow over said overflow wall.

18. Apparatus for separating finely divided solids from suspension in a liquid only slightly lighter than said solids, comprising: a main tank having a bottom outlet; a baflle in said tank spaced above the bottom of the tank dividing the tank into a flotation compartment and an overflow compartment; means for feeding said suspension into said flotation compartment; trough means in said flotation compartment; means for continuously draining said trough means; means to skim flotation mud in said flotation compartment into said trough means; an overflow wall for discharge flow of clarified liquid from said overflow compartment, said overflow wall determining the approxi- 14 mate liquid level in the tank; an overflow tank at approximately the level of the top of said overflow wall with the bottom of the overflow tanl: below said level, said overflow tank having two ports below said level; means connecting one of said two ports with said bottom outlet of the main tank for sedimentary flow from the main tank to the overflow tank, the other of said ports serving for discharge flow from the overflow tank; and passagemeans in said overflow tank connected with one of said ports, the upper end of said passage means being open and at approximately said level, said passage means being adjustable with respect to said level to vary the rate of sedimentary flow'out of the main tank into said overflow tank relative to the rate of overflow out of said overflow compartment of the main tank over said overflow wall.

19. Apparatus as set forth in claim 18 in which said overflow wall is of notched configuration along its upper overflow edge.

' References Cited in the file of this patent UNITED STATES PATENTS 1,310,051 Blomfield July 15, 1919 1,342,115 Janney -2. June 1, 1920 1,366,767 Callow Jan. 25, 1921 1,378,920 Towne et'al May 24, 1921 2,261,487 Scott et al. Nov. 4, 1941 2,324,400 Kelly et al. July 13, 1943 2,364,022 Gillard Nov. 28, 1944 2,375,282 Clemens May 8, 1945 2,418,950 Montgomery Apr. 15, 1947 2,464,707 Montgomery et a1. 4-..- Mar. 15, 1949 2,483,706 Lind Oct. 4, 1949 2,569,141 Bakels Sept. 25, 1951- 2,611,489 Scott Sept. 23, 1952 

1. APPARATUS FOR SEPARATING FINELY DIVIDED SOLIDS FROM SUSPENSION IN A LIQUID ONLY SLIGHTLY LIGHTER THAN SAID SOLIDS, COMPRISING: A RELATIVELY WIDE, OPEN, CYLINDRICAL TANK HAVING A VERTICAL WALL AND A BOTTOM OUTLET; A BAFFLE RING CONCENTRIC WITH SAID WALL AND DIVIDING A CYLINDRICAL INNER COMPARTMENT FROM AN ANNULAR OUTER COMPARTMENT, SAID RING EXTENDING ABOVE THE LIQUID LEVEL IN SAID TANK AND BEING SPACED FROM THE TANK BOTTOM; A PLURALITY OF FLOTATION MUD RECEIVING TROUGHS RADIALLY ARRANGED IN SPACED RELATION WITHIN SAID ANNULAR COMPARTMENT AND MEANS FOR CONTINUOUSLY DRAINING SAID TROUGHS; MEANS FOR FEEDING SAID SUSPENSION INTO SAID ANNULAR COMPARTMENT BETWEEN SAID TROUGHS; A PLURALITY OF SKIMMERS ARRANGED WITHIN SAID ANNULAR COMPARTMENT AND MEANS FOR CAUSING SAID SKIMMERS TO ROTATE AROUND THE AXIS OF SAID TANK TO URGE FLOTATION MUD INTO SAID TROUGHS; MEANS FOR CONTINUOUSLY DRAINING CLARIFIED LIQUID FROM THE UPPER SIDE OF THE LIQUID BODY IN SAID CYLINDRICAL INNER COMPARTMENT; MEANS FOR CONTINUOUSLY SWEEPING SEDIMENT COLLECTING ON THE BOTTOM OF SAID TANK TO SAID OUTLET, AND MEANS FOR CONTINUOUSLY WITHDRAWING SAID SEDIMENT FROM SAID OUTLET WHILE MAINTAINING A SUBSTANTIALLY CONSTANT LIQUID LEVEL IN SAID TANK. 